CN115259660A

CN115259660A - Glass substrate

Info

Publication number: CN115259660A
Application number: CN202210983759.0A
Authority: CN
Inventors: 齐藤敦己
Original assignee: Nippon Electric Glass Co Ltd
Current assignee: Nippon Electric Glass Co Ltd
Priority date: 2017-04-27
Filing date: 2018-04-12
Publication date: 2022-11-01
Anticipated expiration: 2038-04-12
Also published as: CN115259660B; WO2018198804A1; JP7226508B2; JP2022010144A; US20220363585A1

Abstract

The glass substrate of the present invention is characterized by a high temperature viscosity of 10 ^2.5 The temperature at dPa.s is less than 1650 ℃, and the temperature is measured by Log eta ₅₀₀ Estimated viscosity Log η at 500 ℃ calculated as =0.167 × Ps-0.015 × Ta-0.062 × Ts-18.5 ₅₀₀ Is 26.0 or more.

Description

Glass substrate

The application is divisional application of patent application with application numbers of 201880023944.7, application dates of 2018, 4 months and 12 days and the name of 'glass substrate'.

Technical Field

The present invention relates to a glass substrate, and more particularly to a glass substrate suitable for a substrate of a flat panel display such as a liquid crystal display and an organic EL display.

Background

Organic EL devices such as organic EL displays are thin, excellent in video display, and low in power consumption, and therefore are used for displays of mobile phones and the like.

As a substrate of an organic EL display, a glass substrate is widely used. Glass substrates for this use are those which do not substantially contain alkali metal oxides or which contain a small amount of alkali metal oxides. In other words, the glass substrate for this use uses a low alkali glass. When the low alkali glass is used, alkali ions can be prevented from diffusing into the semiconductor material produced in the heat treatment step.

In recent years, high-definition displays have been required for smart phones and mobile terminals, and LTPS (Low-temperature poly silicon) TFTs and oxide TFTs have been used as semiconductors of Thin Film Transistors (TFTs) for driving.

Disclosure of Invention

Problems to be solved by the invention

The glass substrate for this use requires, for example, the following characteristics (1) and (2).

(1) Thin glass substrates have high productivity, particularly high melting properties and fining properties.

(2) In the manufacture of LTPS TFT and oxide TFT, the heat treatment temperature is higher than that of conventional amorphous Si TFT. Therefore, the heat resistance is higher than that of the conventional one in order to reduce the heat shrinkage of the glass substrate.

However, it is not easy to satisfy the above-mentioned required characteristics (1) and (2). That is, if the heat resistance of the glass substrate is to be improved, productivity (meltability, fining) tends to be reduced, and conversely, if the productivity of the glass substrate is to be improved, the heat resistance tends to be reduced.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a glass substrate that can achieve both productivity and heat resistance.

Means for solving the problems

The present inventors have found that the above technical problem can be solved by limiting the viscosity characteristics of the glass substrate to a predetermined range, and have proposed the present invention. The glass substrate of the present invention is characterized by a high temperature viscosity of 10 ^2.5 The temperature at dPa · s is 1670 ℃ or less, and the estimated viscosity Log η at 500 ℃ calculated by the following formula 1 ₅₀₀ Is 26.0 or more. Here, "10" is ^2.5 The temperature "at dPa · s" can be measured by the platinum ball pulling method. "Strain Point", "annealing Point" and "softening Point" refer to compositions based on ASTM C336,The values measured by the method of ASTM C338.

[ formula 1]

Logη ₅₀₀ ＝0.167×Ps-0.015×Ta-0.062×Ts-18.5

Ps: strain point (. Degree. C.)

Ta: annealing Point (. Degree.C.)

Ts: softening Point (. Degree. C.)

The heat resistance of a glass substrate has been evaluated by temperatures such as strain point and annealing point which can be measured. However, these temperature ranges are about 200 ℃ higher or higher than the process temperature for manufacturing LTPS · TFTs and oxide TFTs. Therefore, the temperature of the strain point, annealing point, or the like cannot be evaluated accurately.

The present inventors have repeatedly conducted various experiments and, as a result, found that: the estimated viscosity at 500 ℃ close to the process temperature for manufacturing the LTPS TFT or the oxide TFT is calculated, and if this is used as an index of heat resistance, the heat resistance of the glass substrate can be accurately evaluated.

The present inventors have also found that even if the strain point, which is an index of the past, is the same, the heat resistance is greatly different. Table 1 shows the estimated viscosity Log η at 500 deg.C ₅₀₀ Data relating to heat shrinkage. The glass composition and the strain point Ps are the same for the glass substrate P and the glass substrate Q. As can be seen from Table 1, the estimated viscosity Log η at 500 ℃ of the glass substrate P ₅₀₀ 27.8, a thermal shrinkage of 17.5ppm, and a viscosity Log η estimated at 500 ℃ of the glass substrate Q ₅₀₀ 29.1 and a heat shrinkage of 12.8ppm. In other words, for the glass substrate P and the glass substrate Q, even if the glass composition and the strain point Ps were the same, the thermal shrinkage rates differed by 4.7ppm. Considering that the heat shrinkage ratio of the glass substrate for a high definition display is particularly preferably 18ppm or less, it can be said that the difference of 4.7ppm is very large. Further, the estimated viscosity Log η at 500 ℃ is determined ₅₀₀ As an index, the difference can be estimated accurately. Here, the "heat shrinkage rate" is a value calculated as follows. First, a linear mark is marked at a predetermined position of a sample, and the sample is folded perpendicularly to the mark and divided into two glass pieces. Then, only one is neededThe glass sheet was subjected to a predetermined heat treatment (heating at 5 ℃ C./min from room temperature, holding at 500 ℃ C. For 1 hour, and cooling at 5 ℃ C./min). Then, the heat-treated glass sheet and the glass sheet which was not heat-treated were aligned and fixed by an adhesive tape T, and then the shift of the mark was measured. The shift of the mark is set to be Delta L, and the length of the sample before heat treatment is set to be L ₀ When using Δ L/L ₀ The heat shrinkage was calculated by the following formula (unit: ppm).

[ Table 1]

	P	Q
			Ps[℃]	740	740
Thermal shrinkage [ ppm ]]	17.5	12.8
			Log η poise at 500 DEG C]	27.8	29.1

Here, in consideration of the above, the estimated viscosity Log η of the glass substrate of the present invention at 500 ℃ is ₅₀₀ The limit is 26.0 or more. This can improve the heat resistance of the glass substrate.

On the other hand, if the high melting point component is made largeThe amount of the viscosity Log η can be adjusted to 500 ℃ by introducing the amount into the glass composition ₅₀₀ However, in this case, the meltability and the fining property are reduced, and the productivity of the glass substrate is reduced. Here, the glass substrate of the present invention is obtained by forming a glass substrate having a high-temperature viscosity of 10 ^2.5 The temperature at dPa · s is limited to 1670 ℃ or less, thereby preventing the above.

In addition, the glass substrate of the present invention preferably has an a value of 25.0 or more, which is calculated by the following formula 2.

[ formula 2]

A value = Log η ₅₀₀ - [ beta-OH value (mm) ^-1 )]×[B ₂ O ₃ (mass%)]

Here, the "β -OH value" is a value calculated from the following formula 3 using FT-IR.

[ formula 3]

beta-OH value = (1/X) log (T) ₁ /T ₂ )

X: plate thickness (mm)

T ₁ : reference wavelength 3846cm ^-1 Transmittance (%) of

T ₂ : hydroxyl absorption wavelength of 3600cm ^-1 Near minimum transmittance (%)

The glass substrate of the present invention preferably has a β -OH value of 0.20/mm or less.

The glass substrate of the present invention preferably has a β -OH value of 0.15/mm or less.

In addition, the glass substrate of the present invention is preferably B in the glass composition ₂ O ₃ The content of (B) is less than 2.0 mass%.

The glass substrate of the present invention preferably contains 55 to 65% by mass of SiO as a glass composition ₂ 16 to 22 percent of Al ₂ O ₃ 0 to 1% of B ₂ O ₃ 0 to less than 0.1% of Li ₂ O+Na ₂ O+K ₂ O, 1 to 6 percent of MgO, 2 to 8 percent of CaO, 0 to 2 percent of SrO, 4 to 13 percent of BaO and 0 to less than 0.010 percent of As ₂

O

₃ 0 to less than 0.010% of Sb ₂ O ₃ 。

In addition, the glass substrate of the present invention is preferably made of glassFe in (B) ₂ O ₃ The content of (B) is 0.010 mass% or less.

The glass substrate of the present invention preferably has a liquidus temperature of 1300 ℃ or lower. The "liquidus temperature" herein means a temperature at which devitrification (devitrification crystal) is observed in glass when the glass powder remaining in a 50 mesh (300 μm) is put into a platinum boat through a standard sieve of 30 mesh (500 μm), and then held in a temperature gradient furnace for 24 hours, and then the platinum boat is taken out.

The glass substrate of the present invention is preferably formed by an overflow down-draw method, in other words, by having a forming converging surface in the center of the thickness of the glass substrate. Here, the "overflow drawing method" is a method in which: molten glass is caused to overflow from both sides of a heat-resistant chute-like structure, and the overflowing molten glass is caused to merge at the lower end of the chute-like structure and to extend downward to form a glass substrate.

In addition, the glass substrate of the present invention is preferably used for a substrate of an organic EL device.

Drawings

Fig. 1 is data showing a relationship between the a value and the heat shrinkage ratio.

Detailed Description

In the glass substrate of the present invention, the high temperature viscosity is 10 ^2.5 The temperature at the time of mooring is 1670 ℃ or lower, preferably 1650 ℃ or lower, 1640 ℃ or lower, 1630 ℃ or lower, and particularly preferably 1500 to 1620 ℃. If 10 ^2.5 When the temperature at the bottom is high, the meltability and the clarity are reduced, and the production cost of the glass substrate increases.

In the glass substrate of the present invention, the estimated viscosity Log η at 500 ℃ is ₅₀₀ Is 26.0 or more, preferably 28.0 or more, 28.5 or more, 29.0 or more, and particularly preferably 29.5 to 35. If the estimated viscosity Log η at 500 ℃ is ₅₀₀ If the amount is too low, the heat resistance of the glass substrate decreases, and the thermal shrinkage of the glass substrate increases.

According to the investigation of the present inventors, it was found that the a value = Log η ₅₀₀ - [ beta-OH value]×(B ₂ O ₃ Content (b) shows a high correlation with the measured value of the heat shrinkage rate, and when the value a is large, the heat shrinkage rate becomes small. FIG. 1 shows the A value and the heat shrinkageData of the relationship of (a). In the glass substrate of the present invention, the value a is preferably 25.0 or more, 27.0 or more, 28.0 or more, 29.0 or more, and particularly preferably 30.0 to 40.0. If the value a is too small, the heat resistance of the glass substrate is lowered, and the thermal shrinkage rate of the glass substrate is likely to increase.

From the formula 3, it is understood that the water present in a small amount in the glass affects the relaxation behavior of the glass. The relaxation is a rapid relaxation different from a slow relaxation governed by viscosity, and the rate of rapid relaxation gradually increases as the thermal shrinkage rate decreases. This rapid relaxation is likely to occur when the amount of water in the glass increases. Therefore, as the amount of water in the glass is smaller, rapid relaxation is more difficult to occur, and the effect of reducing the thermal shrinkage rate is relatively high in a glass region having a low thermal shrinkage rate as in the glass substrate of the present invention. Therefore, the β -OH value is preferably 0.20/mm or less, 0.15/mm or less, 0.12/mm or less, 0.11/mm or less, 0.10/mm or less, 0.09/mm or less, 0.07/mm or less, and particularly preferably 0.01 to 0.05/mm.

As a method for reducing the β -OH value, there are the following methods (1) to (7), among which the methods (1) to (4) are effective. (1) selecting a raw material with a low water content. (2) Adding Cl and SO into glass batch ₃ And the like. And (3) heating by electrifying through the heating electrode. And (4) adopting a small melting furnace. (5) the amount of water in the furnace atmosphere is reduced. (6) N in molten glass ₂ And (4) bubbling. (7) increasing the flow rate of the molten glass.

As shown in formula 3, B in the glass composition ₂ O ₃ The smaller the content of (b), the lower the heat shrinkage ratio. This is because B ₂ O ₃ The smaller the content of (b), the more easily the state of low moisture content in the glass can be maintained. Specifically, if B ₂ O ₃ Particularly, if the glass contains a large amount of tridentate boron, the solubility of water increases, and it is difficult to maintain the state where the water content in the glass is low. Therefore, in the glass substrate of the present invention, B in the glass composition ₂ O ₃ The content of (b) is preferably 2% by mass or less, 1.5% by mass or less, 1% by mass or less, and less than 1.0% by mass, and particularly preferably 0.1 to 0.9% by mass.

Glass of the inventionThe glass substrate preferably contains 55 to 65% by mass of SiO as a glass composition ₂ 16 to 22% of Al ₂ O ₃ 0 to 1% of B ₂ O ₃ 0 to less than 0.1% of Li ₂ O+Na ₂ O+K ₂ O, 1 to 6 percent of MgO, 2 to 8 percent of CaO, 0 to 2 percent of SrO, 4 to 13 percent of BaO and 0 to less than 0.010 percent of As ₂

O

₃ 0 to less than 0.010% of Sb ₂ O ₃ . The reason why the contents of the respective components are limited as described above will be described below. In the description of the content of each component,% represents mass%.

SiO ₂ The lower limit range of (a) is 55% or more, 56% or more, 57% or more, 58% or more, particularly 59% or more, and the upper limit range of (b) is preferably 65% or less, 64% or less, 63% or less, particularly 62% or less. If SiO ₂ If the content of (B) is too small, al-containing particles tend to be formed ₂ O ₃ The strain point is easily lowered at the same time as devitrification crystallization of (2). On the other hand, if SiO ₂ When the content (b) is too large, the high-temperature viscosity increases, the meltability tends to decrease, and devitrified crystals such as cristobalite precipitate, and the liquid phase temperature tends to increase.

Al ₂ O ₃ The lower limit of the range is 16% or more, 17% or more, 18% or more, particularly 18.5% or more, and the upper limit of the range is 22% or less, 21% or less, particularly 20% or less. If Al is present ₂ O ₃ When the content of (b) is too small, the strain point is liable to be lowered, and the glass is liable to be phase-separated. On the other hand, if Al ₂ O ₃ When the content of (b) is too large, devitrification and crystallization of mullite, anorthite, and the like occur, and the liquid phase temperature tends to be high.

Related to B ₂ O ₃ Suitable amounts of (b) are as described above.

As mentioned above, li ₂ O、Na ₂ O and K ₂ O is a component that deteriorates characteristics of the semiconductor film. Thus, li ₂ O、Na ₂ O and K ₂ The total amount of O and the respective content are preferably less than 1.0%, less than 0.50%, less than 0.20%, less than 0.10%, less than 0.08%, in particular less than 0.06% of the total weight of the composition. On the other hand, if a small amount of Li is introduced ₂ O、Na ₂ O and K ₂ O lowers the resistivity of the molten glass, and the glass is easily melted by the energization and heating by the heating electrode. Thus, li ₂ O、Na ₂ O and K ₂ The total amount and the respective contents of O are preferably 0.01% or more, 0.02% or more, 0.03% or more, 0.04% or more, and particularly 0.05% or more. In consideration of the influence on the semiconductor film and the reduction in resistivity, it is preferable that Li be used ₂ O、Na ₂ O and K ₂ Preferential introduction of Na into O ₂ O。

MgO is a component that reduces high-temperature viscosity and improves meltability. The MgO content is preferably 1 to 6%, 2 to 5.5%, 2.5 to 5.5%, particularly 3 to 5%. If the content of MgO is too small, the above-described effects are difficult to obtain. On the other hand, if the content of MgO is too large, the strain point tends to decrease.

CaO is a component that reduces the high-temperature viscosity and improves the meltability without lowering the strain point. In addition, caO is a component in which a relatively low-cost raw material is introduced into an alkaline earth metal oxide, thereby reducing the raw material cost. The content of CaO is preferably 2 to 8%, 3 to 8%, 4 to 9%, 4.5 to 8%, particularly 5 to 7%. If the content of CaO is too small, the above-described effects are difficult to obtain. On the other hand, if the content of CaO is too large, the thermal expansion coefficient becomes too high and the glass is liable to devitrify.

SrO is a component for improving resistance to devitrification, and is a component for improving fusibility by reducing high-temperature viscosity without lowering strain point. The SrO content is preferably 0 to 2%, 0 to 1.5%, 0.1 to 1.5%, 0.2 to 1%, especially 0.3 to less than 1.0%. If the SrO content is too small, it becomes difficult to obtain the effect of suppressing phase separation and the effect of improving resistance to devitrification. On the other hand, if the SrO content is too large, the compositional balance of the glass composition is lost, and the strontium silicate type devitrified crystal is likely to precipitate.

BaO is a component that significantly improves devitrification resistance among alkaline earth metal oxides. The content of BaO is preferably 4 to 13%, 5 to 12%, 6 to 11%, particularly 7 to 10%. If the content of BaO is too small, the liquidus temperature becomes high and the devitrification resistance is liable to decrease. On the other hand, if the content of BaO is too large, the compositional balance of the glass composition is broken, and devitrified crystals containing BaO are likely to precipitate.

RO (the total amount of MgO, caO, srO and BaO) is preferably 10 to 22%, 13 to 21%, 14 to 20%, particularly 15 to 20%. If the RO content is too small, the meltability tends to be low. On the other hand, if the RO content is too high, the compositional balance of the glass composition is lost, and the devitrification resistance is liable to decrease.

As when the glass is melted by the electric heating of the heating electrode without being heated by the combustion flame of the burner ₂ O ₃ 、Sb ₂ O ₃ These are components for coloring glass, and the content is preferably less than 0.010%, particularly preferably less than 0.0050%, respectively.

In addition to the above components, for example, the following components may be added to the glass composition. From the viewpoint of reliably obtaining the effects of the present invention, the content of the other components than the above components is preferably 5% or less, and particularly preferably 3% or less, in total.

ZnO is a component for improving meltability, but if ZnO is contained in a large amount, the glass is easily devitrified, and the strain point is easily lowered. The content of ZnO is preferably 0 to 5%, 0 to 3%, 0 to 0.5%, particularly 0 to 0.2%.

P ₂ O ₅ Is a component for increasing the strain point, but if it contains a large amount of P ₂ O ₅ The glass is easily phase separated. P ₂ O ₅ The content of (B) is preferably 0 to 1.5%, 0 to 1.2%, particularly 0 to 1%.

TiO ₂ Is a component for lowering high-temperature viscosity and improving meltability, and is a component for suppressing negative induction (solarization), but if a large amount of TiO is contained ₂ The glass is colored, and thus the transmittance is easily lowered. Thus, tiO ₂ The content of (B) is preferably 0 to 3%, 0 to 1%, 0 to 0.1%, particularly 0 to 0.02%.

Fe ₂ O ₃ Are inevitably mixed as impurities derived from the glass raw materialThe ingredients are added. In addition, fe ₂ O ₃ In some cases, the glass is expected to be added positively (for example, 0.003% or more, particularly 0.005% or more) as a refining agent or an effect of lowering the resistivity of molten glass. On the other hand, from the viewpoint of improving the transmittance in the ultraviolet region, it is preferable to reduce Fe as much as possible ₂ O ₃ The content of (a). When the transmittance in the ultraviolet region is increased, the irradiation efficiency when the laser beam in the ultraviolet region is used in a process related to a display device can be improved. Thus, fe ₂ O ₃ The content of (b) is preferably 0.020% or less, 0.015% or less, 0.010% or less, and particularly less than 0.010%.

Y ₂ O ₃ 、Nb ₂ O ₅ 、La ₂ O ₃ Has the effects of improving strain point, young's modulus, etc. However, if the content of these components is too large, the density and the raw material cost are liable to increase. Thus, Y ₂ O ₃ 、Nb ₂ O ₅ 、La ₂ O ₃ The content of (b) is preferably 0 to 3%, 0 to 1%, 0 to less than 0.10%, and particularly preferably 0 to less than 0.05%, respectively.

Cl is a component that functions as a drying agent and lowers the β -OH value. Therefore, when Cl is introduced, the lower limit content is preferably 0.001% or more, 0.003% or more, and particularly 0.005% or more. However, if the Cl content is too large, the strain point is easily lowered. Therefore, the upper limit content of C1 is preferably 0.5% or less, 0.2% or less, and particularly 0.08% or less. As a raw material for introducing Cl, a chloride of an alkaline earth metal oxide such as strontium chloride, aluminum chloride, or the like can be used.

SO ₃ Is a component that functions as a desiccant and reduces the beta-OH value. Therefore, in the introduction of SO ₃ In the case of (3), the lower limit content is preferably 0.0001% or more, and more preferably 0.0005% or more. However, if SO ₃ If the content of (b) is too large, reboil bubbles are easily generated. Thus, SO ₃ The upper limit content of (b) is preferably 0.05% or less, 0.01% or less, 0.005% or less, particularly 0.001% or less.

SnO ₂ The component has a good clarifying action in a high temperature region, a high strain point, and a low high temperature viscosity. SnO ₂ The content of (b) is preferably 0 to 1%, 0.001 to 1%, 0.05 to 0.5%, and particularly preferably 0.1 to 0.3%. If SnO ₂ When the content of (B) is too large, snO ₂ Devitrification crystals of (2) are liable to precipitate. If SnO is required ₂ If the content of (b) is less than 0.001%, the above-mentioned effects are hardly obtained.

SnO may also be used as long as it does not significantly impair the glass properties ₂ Other clarifying agents. Specifically, ceO may be added in a total amount ₂ F, C to 1%, for example, and metal powders of Al, si, etc. may be added to 1%, for example, in total.

The glass substrate of the present invention preferably has the following characteristics.

The strain point is preferably 700 ℃ or higher, 720 ℃ or higher, 730 ℃ or higher, 740 ℃ or higher, 750 ℃ or higher, and particularly 760 to 840 ℃. Thus, in the manufacturing process of LTPS TFT and oxide TFT, the heat shrinkage of the glass substrate is easily suppressed.

The liquid phase temperature is preferably 1300 ℃ or lower, 1280 ℃ or lower, 1260 ℃ or lower, 1250 ℃ or lower, and particularly 900 to 1230 ℃. This makes it easy to prevent devitrification crystals from occurring during molding. Further, since the glass substrate is easily formed by the overflow down-draw method, the surface quality of the glass substrate can be improved. The liquidus temperature is an index of resistance to devitrification, and the lower the liquidus temperature, the more excellent the resistance to devitrification.

The viscosity at the liquidus temperature is preferably 10 ^4.8 Poise above, 10 ^5.0 Poo Yuan, 10 ^5.3 Poise or higher, in particular 10 ^5.5 ～10 ^7.0 Poise. This makes it easy to prevent devitrification and crystallization from occurring during molding. Further, since the glass substrate is easily formed by the overflow down-draw method, the surface quality of the glass substrate can be improved. The "viscosity at liquidus temperature" can be measured by the platinum ball pulling method.

The heat shrinkage at a temperature rise from room temperature at a rate of 5 ℃/min, holding at 500 ℃ for 1 hour, and a temperature drop at a rate of 5 ℃/min is preferably 21ppm or less, 18ppm or less, 15ppm or less, 12ppm or less, particularly 1 to 10ppm. When the heat shrinkage ratio is large, the production yield of high-definition panels tends to decrease.

In the glass substrate of the present invention, the plate thickness is preferably 0.05 to 0.7mm, 0.1 to 0.5mm, particularly 0.2 to 0.4mm. As the thickness is smaller, the weight and thickness of the display can be reduced more easily. In addition, although the necessity of increasing the forming speed (sheet drawing speed) becomes high when the sheet thickness is small, in this case, the thermal shrinkage of the glass substrate tends to increase, in the present invention, since the heat resistance is high, even if the forming speed (sheet drawing speed) is high, the above can be effectively suppressed.

The glass substrate of the present invention is preferably formed by an overflow down-draw method, in other words, by having a forming converging surface in the center of the thickness of the glass substrate. In the overflow down-draw method, the surface to be the surface of the glass substrate is formed in a free surface state without being in contact with the trough-shaped refractory. Therefore, a glass substrate having good surface quality without polishing can be produced at low cost. In addition, the overflow down-draw method also has such an advantage that a thin glass substrate is easily formed.

The manufacturing process of the glass substrate generally includes: a blending step, a melting step, a clarifying step, a supplying step, a stirring step, and a forming step. The blending step is a step of blending glass raw materials to produce a glass batch. The melting step is a step of obtaining molten glass by melting a batch of glass. The fining step is a step of fining the molten glass obtained in the melting step by the action of a fining agent or the like. The supply step is a step of transferring the molten glass between the steps. The stirring step is a step of stirring and homogenizing the molten glass. The forming step is a step of forming the molten glass into a plate shape. If necessary, a step other than the above-described step, for example, a state adjustment step of adjusting the molten glass to a state suitable for the molding state may be introduced after the stirring step.

Low alkali glass is generally melted by heating by combustion in a burner. The burner is generally disposed above the melting furnace, and fossil fuel, specifically, liquid fuel such as heavy oil, gas fuel such as LPG, or the like is used as fuel. The combustion flame can be obtained by burning a mixed gas of a fossil fuel and oxygen.

However, in the combustion heating by the burner, a large amount of water is mixed into the molten glass, and thus the β — OH value of the glass substrate tends to increase. Therefore, as a method for industrially producing the glass substrate of the present invention, it is preferable to subject a glass batch to electric heating by a heating electrode. In this way, the temperature of the molten glass is lowered from the bottom surface of the melting furnace toward the upper surface of the melting furnace by the energization heating of the heating electrodes provided on the wall surface of the melting furnace, and therefore a large amount of glass batches in a solid state are present on the liquid surface of the molten glass in the melting furnace. As a result, the moisture adhering to the glass batch in a solid state evaporates, and an increase in the amount of moisture due to the raw material can be suppressed. Further, when the heating electrode is used for the electric heating, the energy per unit mass for obtaining the molten glass is reduced, and the amount of the volatile matter to be melted is reduced, so that the environmental load can be reduced.

As a method for industrially producing the glass substrate of the present invention, it is more preferable to perform energization heating by a heating electrode without performing combustion heating by a burner. When the combustion heating is performed by a burner, moisture generated during the combustion of fossil fuel is easily mixed into the molten glass. Therefore, the β -OH value of the molten glass is easily reduced without performing combustion heating by a burner. Note that "the heating electrode performs the energization heating without performing the combustion heating by the burner" means that the glass batch is continuously melted by performing the energization heating only by the heating electrode, but the following cases are excluded: for example, when combustion heating is performed by a burner at the time of starting the melting furnace, combustion heating by the burner is performed locally and secondarily at a specific portion of the melting furnace.

The heating by the heating electrode is preferably performed by applying an ac voltage to the heating electrode provided at the bottom or side of the melting furnace so as to contact the molten glass in the melting furnace. The material for the heating electrode preferably has heat resistance and corrosion resistance against molten glass, and for example, tin oxide, molybdenum, platinum, rhodium, or the like can be used. Molybdenum is particularly preferable because it has high heat resistance and high degree of freedom in installation in a melting furnace.

The low alkali glass has a high specific resistance because of a small content of alkali metal oxide. Therefore, when the electric heating by the heating electrode is applied to the low alkali glass, the electric current flows not only through the molten glass but also through the refractory constituting the melting furnace, and there is a possibility that the refractory is damaged more rapidly. In order to prevent this, as the furnace refractory, a zirconia-based refractory having high resistivity is preferably used, and particularly, a zirconia fused brick is preferable, and as described above, a component (Li) which lowers resistivity is also preferable ₂ O、Na ₂ O、K ₂ O、Fe ₂ O ₃ Etc.) are introduced into the molten glass in small amounts. ZrO in the zirconia-based refractory ₂ The content of (b) is preferably 85% by mass or more, particularly 90% by mass or more.

Examples

The present invention will be described below based on examples. However, the following examples are only illustrative. The present invention is not limited in any way by the following examples.

Table 2 shows examples (sample Nos. 1 to 6) and comparative examples (sample Nos. 7 to 9) of the present invention.

[ Table 2]

First, in order to obtain the glass composition and β — OH value shown in the table, a glass batch after blending was charged into a small-sized test melting furnace constructed of zirconia electrocast bricks, and then, the glass batch was melted at 1600 to 1650 ℃ by energization heating with a molybdenum electrode without heating with a combustion flame of a burner. In samples nos. 1 to 6, the burners were used only when the melting furnace started to operate, and were stopped after molten glass was produced. As to samples No.7 to 9, heating by a combustion flame of an oxygen burner and energization by a heating electrode were simultaneously employedAnd melted by electrical heating. Next, the molten glass was refined and stirred in a Pt — Rh vessel, and then supplied to a zircon forming body, and formed into a flat plate shape having a thickness of 0.5mm by an overflow down-draw method. The resulting glass substrate was evaluated for the beta-OH value, the thermal shrinkage rate, and the estimated viscosity Log eta at 500 ℃ ₅₀₀ Strain point Ps, annealing point Ta, softening point Ts, 10 ^4.0 Temperature at viscosity of poise, 10 ^3.0 Temperature at viscosity of poise, 10 ^2.5 Temperature at viscosity of poise, liquidus temperature TL, viscosity log η TL at liquidus temperature, and A value.

Estimated viscosity Log η at 500 deg.C ₅₀₀ Is a value calculated from the above equation 1.

The value a is a value calculated from the above equation 2.

The heat shrinkage ratio is a value calculated as follows. First, a linear mark is marked at a predetermined position of a sample, and the sample is folded perpendicularly to the mark and divided into two glass pieces. Then, only one of the glass sheets was subjected to a predetermined heat treatment (heating at a rate of 5 ℃/min from room temperature, holding at 500 ℃ for 1 hour, and cooling at a rate of 5 ℃/min). Then, the heat-treated glass sheet and the glass sheet which was not heat-treated were aligned and fixed by an adhesive tape T, and then the shift of the mark was measured. The shift of the mark is set to be Delta L, and the length of the sample before heat treatment is set to be L ₀ When using Δ L/L ₀ The heat shrinkage was calculated by the following formula (unit: ppm).

The β -OH value is a value calculated from the above formula 3 using FT-IR.

The strain point Ps, annealing point Ta, and softening point Ts are values measured by the methods of ASTM C336 and ASTM C338.

High temperature viscosity 10 ^4.0 Poise 10 ^3.0 Poise 10 ^2.5 The temperature at poise is a value measured by the platinum ball pulling method.

The liquidus temperature TL is as follows: the temperature at which crystals precipitated was measured by placing the glass powder remaining in a 50 mesh (300 μm) screen through a standard 30 mesh (500 μm) platinum boat and then holding the boat in a temperature gradient furnace for 24 hours. The viscosity log η TL at the liquidus temperature is a value measured by the platinum ball pulling method.

As is clear from Table 2, the estimated viscosity Log η at 500 ℃ of sample Nos. 1 to 6 ₅₀₀ High and high temperature viscosity 10 ^2.5 The temperature at the time of the kneading is low, so that the heat shrinkage is small and the productivity is high. On the other hand, sample No.7 had a high-temperature viscosity of 10 ^2.5 The temperature at the poise is high and therefore the productivity is low. Sample Nos. 8 and 9 had estimated viscosities Log η at 500 ℃ of the respective samples ₅₀₀ Low, and therefore, large in heat shrinkage.

Industrial applicability

The glass substrate of the present invention is suitable for use as a cover glass for an image sensor such as a Charge Coupled Device (CCD) or a constant contact solid-state imaging device (CIS), a substrate for a solar cell, a cover glass, a substrate for organic EL lighting, and the like, in addition to a substrate for a flat panel display such as a liquid crystal display or an organic EL display.

Claims

1. A glass substrate characterized in that a glass substrate,

high temperature viscosity 10 ^2.5 The estimated viscosity Log eta at 500 ℃ calculated from the following formula, wherein the temperature at the time of mooring is 1670 ℃ or less ₅₀₀ The content of the compound is more than 26.0,

Logη ₅₀₀ ＝0.167×Ps-0.015×Ta-0.062×Ts-18.5

ps: strain point (. Degree. C.)

Ta: annealing Point (. Degree. C.)

Ts: softening point (. Degree. C.).

2. Glass substrate according to claim 1,

the A value calculated by the following formula is 25.0 or more,

a value = Log η ₅₀₀ - [ beta-OH value (mm) ^-1 )]×[B ₂ O ₃ (mass%)]。

3. Glass substrate according to claim 1 or 2,

the beta-OH value is less than 0.20/mm.

4. Glass substrate according to any one of claims 1 to 3,

the beta-OH value is less than 0.15/mm.

5. Glass substrate according to any one of claims 1 to 4,

B ₂ O ₃ the content of (B) is less than 2.0 mass%.

6. The glass substrate according to any one of claims 1 to 5,

the glass composition contains 55 to 65 mass% of SiO ₂ 16 to 22 percent of Al ₂ O ₃ 0 to 1% of B ₂ O ₃ 0 to less than 0.1% of Li ₂ O+Na ₂ O+K ₂ O, 1 to 6 percent of MgO, 2 to 8 percent of CaO, 0 to 2 percent of SrO, 4 to 13 percent of BaO and 0 to less than 0.010 percent of As ₂ O ₃ 0 to less than 0.010% of Sb ₂ O ₃ 。

7. Glass substrate according to any one of claims 1 to 6,

fe in glass composition ₂ O ₃ The content of (B) is 0.010 mass% or less.

8. Glass substrate according to any one of claims 1 to 7,

the liquid phase temperature is 1300 ℃ or lower.

9. The glass substrate according to any one of claims 1 to 8,

the plate thickness center part has a forming converging surface.

10. The glass substrate according to any one of claims 1 to 9,

the glass substrate is used for a substrate of an organic EL device.